INTRODUCTION 6 



never is, as he believed, any 'invariable association' between the various 

 parts of mammals. This is because each part is adapted to the particular 

 service which it has to perform for the animal as a whole, service which may 

 be rendered in many different environments and on many different kinds 

 of food. While the feet and limbs are becoming fitted to moving in the 

 water, or on land, in trees or in flight through the air, the teeth at the 

 same time may become fitted to one of many different kinds of food, to 

 shrubs, grasses, bark, insects, or to other animals. Thus, while serving the 

 whole, different parts of animals evolve separately and independently, 

 and there have arisen consequently an almost unlimited number of com- 

 binations of foot, limb, skull, and tooth structure.^ The simple reason why 

 a law conceived by a special creationist is invalid is that while all parts 

 of an animal conspire to make the animal as a whole adaptive, there is 

 no fixed correlation either in the form of the parts or in the speed with 

 which they evolve. 



It is consequently impossible for the palaeontologist to predict the 

 entire structure of an unknown animal from one of its parts only, unless 

 the part happens to belong to a type already very familiar. For example, 

 if we found the fossil claw bone of the cat we would know that it belonged 

 to a cat and would be able to restore the cat; but if we found a claw bear- 

 ing only a general likeness to that of the cat it would be very unsafe to 

 restore the cat. There are herbivorous quadrupeds (fam. Chalicotheriidse) 

 in which the claws remotely resemble those of the giant ground sloths and 

 anteaters; it happened that one of these very claws (of the genus Macro- 

 therium) was brought to Cuvier, and full of confidence in his law, but en- 

 tirely deceived by the resemblance of the claw to that of one of the exist- 

 ing scaly anteaters (the pangolins of Africa and India), he termed the 

 animal Pangolin gigantesque. Had he restored the animal according to 

 his own ' law of correlation, ' he would have pictured a giant anteater of a 

 structure as wide as the poles from what we now know to be the actual 

 form of the quadruped, Macrotherium, which in body, limbs, and teeth is 

 a true herbivore remotely related to the odd-toed quadrupeds known as 

 titanotheres. 



Again, in direct opposition to Cuvier's law we find that certain Ameri- 

 can Eocene monkeys (Notharctus), in which the limbs are fitted to tree- 

 living, or arboreal, habits, exhibit grinding teeth very similar to those of 

 the ground-living Eocene horses (Orohippus), in which the limbs, on the 

 contrary, are distinctly of the running, or cursorial, type. Because of their 

 teeth these monkeys were at first thought to be hoofed animals. Thus 

 teeth do not give us certain indications of the form of the hoofs, nor does 

 the form of the hoof give certain indications of the form of the teeth. 



Evolutionary law of correlation. — Yet despite this independent evolu- 

 tion of parts, every part does conspire to make the animal as a whole adap- 



1 See the Law of Adaptive Radiation, p. 22. 



